Alignment couplings are useful parts of materials testing apparatus. Free swiveling alignment couplings are used above and below a sample to relieve the bending strain on the sample. Double knife edge couplings are commonly used for this purpose. Fixed alignment couplings are used to change the alignment of the load train and keep it in a fixed position.
Alignment fixtures and free moving alignment couplings do not eliminate bending strains. The present invention can be used to reduce the bending strain and, if desired, to subject to the sample to a known bending strain.